Project 3 seeks to understand the longitudinal pattern of behavioral problems in twin children by following up a sample previously systematically ascertained from birth records. The project uses genetic latent class analysis applied to 3-occasion, longitudinal data (age 7-8 years, 12-13 years, and 15-16 years) as a foundation for understanding temperamental and family risk factors, as well as to provide a sample for studying neural correlates of adolescent anxiety in Project 4. We predict that the child's standing on a profile of seven dimensions (depressed, socially anxious, worried/obsessive, inattentive, impulsive, hyperactive, defiant/aggressive/callous) assessed with multiple methods will reveal heterogeneity within existing DSM-IV diagnostic categories and commonality among subgroups of children with different DSM-IV diagnoses. Several risk factors will be examined within the context of latent growth curve analysis, including basal and reactive cortisol patterns studied longitudinally, allelic variants of 8 genes, family stress and observed family interaction patterns, pregnancy and birth complications, and childhood temperament. Operationally, the project involves conducting telephone interviews of both twins and their mothers for a sample over 1,200 twins and their mothers, extensive statistical analyses of the longitudinal data, and a laboratory-based assessment of a subsample who qualify for a diagnosis of anxiety disorder or depression. The laboratory-based assessment battery will include a structured psychiatric interview, cognitive/affective assessments (reaction time and other performance-based measures), and the Trier Social Stress Test as protocol to activate the HPA axis. Results should improve understanding of (1) nosology of childhood anxiety problems;(2) how risk factors act over a substantial period of childhood and adolescence;and (3) cognitive and other processes that may form the substrate of anxious behavior.